A fluid flow system, such as an engine exhaust system, often includes multiple fluid passages configured to direct fluids from a fluid source to a fluid flow outlet. Some fluid passages may also be configured to direct fluids (e.g., gases) toward one or more components or systems coupled to the fluid flow system. In the example of the engine exhaust system, exhaust gas may be directed to an exhaust gas heat recovery (EGHR) system. The EGHR system may include a heat exchanger configured to receive hot exhaust gases from a first exhaust passage, and to return cooled exhaust gases to the exhaust system through a second exhaust passage. The first exhaust passage may form a junction with a bypass passage configured to flow gases past the heat exchanger, and a device configured to control a direction of exhaust gas flow may be positioned within the junction. In some examples, the device may include one or more apertures configured to open or close in order to increase or decrease an amount of gas flowing through the device, thereby adjusting a flow rate of gases through the exhaust system and to the heat exchanger.
Other attempts to address adjusting a flow rate of gases through a fluid flow system include utilizing a plurality of flow control doors. One example approach is shown by Knafl et al. in U.S. Pat. No. 7,921,828. Therein, a heat exchanger of a motor vehicle is disclosed, with the heat exchanger including a plurality of flow control doors adjustable by a control system. The control system may increase or decrease an amount of opening of each flow control door to control an amount of gas flowing into the heat exchanger.
However, the inventors herein have recognized potential issues with such systems. As one example, gas flowing into a heat exchanger (such as that described above) may increase an amount of gas backpressure at an inlet of the heat exchanger beyond an acceptable amount of backpressure for engine operation. In order to reduce gas backpressure, a flow rate of gas into the heat exchanger may be decreased while a flow rate of gas through a bypass passage around the heat exchanger may be increased (in one example, by adjusting an amount of opening of the flow control doors described above). However, when backpressure and/or flow rate is sufficiently high, an amount of force to adjust the opening of the flow control doors may exceed a maximum amount that an actuator of the flow control doors can produce. In other words, the actuator of the flow control doors may not be able to adjust the amount of opening of the flow control doors as a result of the backpressure, and the flow control doors may become stuck in their positions, thereby reducing an amount of control of the control system over the gas flow through the heat exchanger. As a result, engine performance may be decreased.
In one example, the issues described above may be addressed by a method for a door for a fluid flow system, comprising: a pivotable outer door coupled to a fluid passage at a first pivot location; and an inner door positioned within the outer door and pivotable relative to the outer door, with the inner door coupled to the outer door at a second pivot location. In this way, the outer door may pivot in a first direction while the inner door may pivot independently of the outer door in a second direction.
As one example, the door may be positioned at a junction between a bypass fluid passage and an active fluid passage. The door may pivot from a first location corresponding to a bypass position, to a second location corresponding to an active position. In the bypass position, the position of the door may increase a flow of fluid through the bypass fluid passage reduce a flow of fluid through the active fluid passage. In the active position, the door may increase the flow of fluid through the active fluid passage, and decrease the flow of fluid through the bypass fluid passage. If a pressure difference between a first fluid pressure at a first side of the door and a second fluid pressure at a second side of the door exceeds a threshold difference, the inner door may pivot relative to the outer door to increase a flow of fluid through an aperture of the outer door.
In this way, when the pressure difference exceeds the threshold difference while the door is in the active position, the inner door may pivot to direct fluid away from the active fluid passage and into the bypass passage by increasing an amount of opening of the aperture of the outer door, thereby reducing the pressure difference. By reducing the pressure difference, an actuator of the door may then move the door from the active position to the bypass position with reduced effort, thereby reducing a likelihood of the door becoming stuck in the active position. As a result, a reliability of the door is increased, and a door actuator with a smaller size and/or cost may be utilized.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.